A differential operational amplifier (op-amp), which is often referred to as a differential amplifier or an op-amp voltage comparator, is a high-gain electronic voltage amplifier that receives an input voltage and a reference voltage and outputs an output voltage that is typically many times larger than the difference between the input voltage and the output voltage. The output voltage can be processed by an output buffer that converts the output voltage into a digital output signal indicative of whether or not the input voltage is above or below the reference voltage. For example, a digital output signal with a high value (i.e., a “1” value) can indicate that the input voltage is above the reference voltage and a digital output signal with a low value (i.e., a “0” value) can indicate that the input voltage is below the reference voltage. Thus, the digital output signal changes with the difference between the input voltage and output voltage crosses through 0V. Current state of the art op-amps can respond to voltage differences between the input voltage and reference voltage of only a few millivolts (mV). As a result, these op-amps are susceptible to noise glitches. Specifically, small fluctuations due to noise can cause the digital output signal to repeatedly swing from low to high and vice versa (i.e., to chatter). This chatter can propagate into logic circuits that are down stream of the op-amp and can, thus, cause errors. Additionally, this chatter can cause an increase in power consumption.
Consequently, hysteresis is often added to the op-amp circuitry in an attempt to prevent unwanted switching of the digital output signal due to noise. For example, instead of allowing switching to occur whenever the voltage difference passes through 0V, rising and/or falling voltage trip points are used. With a rising voltage trip point, the digital output signal will only switch to high, when the input voltage is some number of millivolts above the reference voltage. With a falling voltage trip point the digital output signal will only switch to low, when the input voltage is some number of millivolts below the reference voltage. Unfortunately, op-amp configurations that enable the use of rising and/or falling voltage trip points are often sensitive to power-voltage-temperature (PVT) variations, which make the trip point(s) unpredictable.